The Effect of Using Palm Kernel Shell Ash and Rice Husk Ash on Geopolymer ConcreteHarianto Hardjasaputra, Ivan Fernando, Judith Indrajaya, Melanie Cornelia and RachmansyahMATEC Web Conf., 251 (2018) 01044DOI: https://doi.org/10.1051/matecconf/201825101044